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Simplify locale parser (#5313)
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This keeps track of slices instead of indices during parsing, and also
simplifies the parser, which removes some checks that were done
redundantly before, which should improve performance.
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@robertbastian
robertbastian authored Jul 31, 2024
1 parent f5b9401 commit cb02882
Showing 1 changed file with 47 additions and 90 deletions.
137 changes: 47 additions & 90 deletions components/locale_core/src/parser/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,40 +17,19 @@ pub use locale::{
parse_locale, parse_locale_with_single_variant_single_keyword_unicode_keyword_extension,
};

#[inline]
const fn is_separator(slice: &[u8], idx: usize) -> bool {
#[allow(clippy::indexing_slicing)]
let b = slice[idx];
b == b'-' || b == b'_'
}

const fn get_current_subtag(slice: &[u8], idx: usize) -> (usize, usize) {
debug_assert!(idx < slice.len());

// This function is called only on the idx == 0 or on a separator.
let (start, mut end) = if is_separator(slice, idx) {
// If it's a separator, set the start to idx+1 and advance the idx to the next char.
(idx + 1, idx + 1)
} else {
// If it's idx=0, end is set to 1
debug_assert!(idx == 0);
(0, 1)
};
const fn skip_before_separator(slice: &[u8]) -> &[u8] {
let mut end = 0;

while end < slice.len() && !is_separator(slice, end) {
#[allow(clippy::indexing_slicing)] // very protected, should optimize out
while end < slice.len() && !matches!(slice[end], b'-' | b'_') {
// Advance until we reach end of slice or a separator.
end += 1;
}
// Notice: this slice may be empty (start == end) for cases like `"en-"` or `"en--US"`
(start, end)
}

pub const fn split_out_range(slice: &[u8], start: usize, end: usize) -> &[u8] {
assert!(start <= slice.len());
assert!(end <= slice.len());
assert!(start <= end);
// SAFETY: assertions and align = size = 1.
unsafe { core::slice::from_raw_parts(slice.as_ptr().add(start), end - start) }
// Notice: this slice may be empty for cases like `"en-"` or `"en--US"`
// MSRV 1.71/1.79: Use split_at/split_at_unchecked
// SAFETY: end < slice.len() by while loop
unsafe { core::slice::from_raw_parts(slice.as_ptr(), end) }
}

// `SubtagIterator` is a helper iterator for [`LanguageIdentifier`] and [`Locale`] parsing.
Expand All @@ -67,46 +46,43 @@ pub const fn split_out_range(slice: &[u8], start: usize, end: usize) -> &[u8] {
// All methods return an `Option` of a `Result`.
#[derive(Copy, Clone, Debug)]
pub struct SubtagIterator<'a> {
pub slice: &'a [u8],
done: bool,
// done + subtag is faster than Option<(usize, usize)>
// at the time of writing.
subtag: (usize, usize),
remaining: &'a [u8],
// current is a prefix of remaning
current: Option<&'a [u8]>,
}

impl<'a> SubtagIterator<'a> {
pub const fn new(slice: &'a [u8]) -> Self {
let subtag = if slice.is_empty() || is_separator(slice, 0) {
// This returns (0, 0) which returns Some(b"") for slices like `"-en"` or `"-"`
(0, 0)
} else {
get_current_subtag(slice, 0)
};
pub const fn new(rest: &'a [u8]) -> Self {
Self {
slice,
done: false,
subtag,
remaining: rest,
current: Some(skip_before_separator(rest)),
}
}

pub const fn next_const(mut self) -> (Self, Option<&'a [u8]>) {
if self.done {
let Some(result) = self.current else {
return (self, None);
}
let result = self.subtag;
if result.1 < self.slice.len() {
self.subtag = get_current_subtag(self.slice, result.1);
};

self.current = if result.len() < self.remaining.len() {
// If there is more after `result`, by construction `current` starts with a separator
// MSRV 1.79: Use split_at_unchecked
// SAFETY: `self.remaining` is strictly longer than `result`
self.remaining = unsafe {
core::slice::from_raw_parts(
self.remaining.as_ptr().add(result.len() + 1),
self.remaining.len() - (result.len() + 1),
)
};
Some(skip_before_separator(self.remaining))
} else {
self.done = true;
}
(self, Some(split_out_range(self.slice, result.0, result.1)))
None
};
(self, Some(result))
}

pub const fn peek(&self) -> Option<&'a [u8]> {
if self.done {
return None;
}
Some(split_out_range(self.slice, self.subtag.0, self.subtag.1))
self.current
}
}

Expand Down Expand Up @@ -189,45 +165,26 @@ mod test {
}

#[test]
fn get_current_subtag_test() {
let slice = "-";
let current = get_current_subtag(slice.as_bytes(), 0);
assert_eq!(current, (1, 1));

let slice = "-en";
let current = get_current_subtag(slice.as_bytes(), 0);
assert_eq!(current, (1, 3));
fn skip_before_separator_test() {
let current = skip_before_separator(b"");
assert_eq!(current, b"");

let slice = "-en-";
let current = get_current_subtag(slice.as_bytes(), 3);
assert_eq!(current, (4, 4));
let current = skip_before_separator(b"en");
assert_eq!(current, b"en");

let slice = "en-";
let current = get_current_subtag(slice.as_bytes(), 0);
assert_eq!(current, (0, 2));
let current = skip_before_separator(b"en-");
assert_eq!(current, b"en");

let current = get_current_subtag(slice.as_bytes(), 2);
assert_eq!(current, (3, 3));
let current = skip_before_separator(b"en--US");
assert_eq!(current, b"en");

let slice = "en--US";
let current = get_current_subtag(slice.as_bytes(), 0);
assert_eq!(current, (0, 2));
let current = skip_before_separator(b"-US");
assert_eq!(current, b"");

let current = get_current_subtag(slice.as_bytes(), 2);
assert_eq!(current, (3, 3));
let current = skip_before_separator(b"US");
assert_eq!(current, b"US");

let current = get_current_subtag(slice.as_bytes(), 3);
assert_eq!(current, (4, 6));

let slice = "--";
let current = get_current_subtag(slice.as_bytes(), 0);
assert_eq!(current, (1, 1));

let current = get_current_subtag(slice.as_bytes(), 1);
assert_eq!(current, (2, 2));

let slice = "-";
let current = get_current_subtag(slice.as_bytes(), 0);
assert_eq!(current, (1, 1));
let current = skip_before_separator(b"-");
assert_eq!(current, b"");
}
}

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